Paints and coatings require the addition of theological additives to prevent the settling of pigments during long periods of storage and to provide leveling and anti-sag properties. Such additives are also utilized to change the viscosity of paints and coatings by thickening or thinning such systems and to impart various other known theological properties. The faster and easier the dispersion characteristics of such additives the better.
It has been known for some time that castor products derived from the castor bean plant and oil obtained from the bean can be formed into a large variety of derivatives; one such example is castor wax. The molecular structure of castor oil permits the creation of a large number of new chemical products by innumerable and various reactions. Many of these derivatives, in combination with extenders, function as excellent theological additives, particularly in aliphatic, enamel and alkyl paint systems. Extenders employed with castor based rheological additives include smectite clays, talcs, aluminum silicate, calcium carbonate, attaplugite clay and various other compositions.
Bentonite and hectorite clays are particularly useful as extenders as are silicates and silica. Extenders are usually present in a range of about 20% to about 80% by weight of the mixture.
A very useful derivative of castor oil for theological additives has proved to be castor wax. U.S. Pat. No. 3,252,820 describes a theological composition containing a thixotrophic wax derived from glyceryl trihydroxystearate, the hydrogenated form of castor oil. Rheox, Inc. offers for sale as a commercial product a theological additive designated THIXCIN R which is based on a castor wax. Rheox also offers for sale products utilizing castor wax and extenders such as clay and aluminum silicate.
Castorwax is a synthetic, waxlike compound obtained by the controlled hydrogenation of natural castor oil. The principal constituent as mentioned above is the glyceride of 12-hydroxystearic acid. There are also present minor quantities of mixed glycerides of this acid and dihydroxystearic and stearic acids.
Castorwax is hard and brittle, and has a high melting point. It is practically odorless (faint fatty or waxy odor) and is tasteless. It can be supplied in the form of uniform, free-flowing, white flakes. The color of sol id castorwax is cream to pearly by reflected light and bluish-white by natural light. When molten it is clear, transparent, very fluid, and largely colorless.
Solid castorwax has an amorphous fracture. It is normally uniform in composition and free from extraneous matter.
Castorwax is relatively non-toxic; it can be considered as having a toxicity on the order of linseed or vegetable oils. Castorwax is extremely hard in comparison with most other waxes. Its penetration value (Penetrometer Needle No. 14 with 100 grams weight) is 0.2 mm as compared with a value of 0.1 for carnauba wax and 1.7 for beeswax.
Castorwax is highly miscible with abietyl alcohol, hydro-abietyl alcohols, chlorinated aromatics, ethyl cellulose, rosin, cellulose acetate butyrate, and polybutyl and polyisobutyl methacrylates. It is moderately miscible with ester gums and coumarone indene resins.
A notable property of castorwax is its relative insolubility in most liquid organic systems at moderate temperatures. Castorwax will dissolve in a number of solvents and oils at elevated temperatures with these solutions on cooling forming gels or paste-like masses.
When castorwax is subjected to elevated temperatures for sustained periods of time it undergoes heat deterioration, so that on cooling, the original wax is found degraded to a stiff paste and eventually, on reheating, to a brown grease.
In addition to fully hydrogenated or regular castorwax, there are also available a series of partially hydrogenated castor oils of intermediate melting points which are wax-like. These waxes of lower melting point may differ in composition from regular castorwax by containing lower percentages of glyceryl trihydroxystearate. As the content of this saturated fatty acid glyceride is reduced, there is a corresponding lowering of the melting point of the product.
Partially hydrogenated castor waxes are slightly more compatible and soluble than fully hydrogenated castorwax. They have utility in those applications where some sacrifice in melting point and hardness can be tolerated to achieve better compatibility and solubility, or where a lower melting point is desired.
Seeding problems have plagued systems using theological additives comprised of castorwax from the very beginning and scientists and technicians have long searched without success for a seed resistant castor product to use as a rheological additive. Seeding occurs because of the forming of colloidal particles in paint containing castor wax products. These colloidal particles result from either solvent-swollen but not properly dispersed grains of castor wax (caused by low heat of activation) or by the precipitation of dissolved wax (caused by overheating). Paint left standing often shows both an increase in the number of such particles and an increase in their size. Paint also may demonstrate such seeding immediately after manufacture.
Seeding is undesirable because such large particles present unpleasant visual qualities after paint and coatings have been applied to a surface. In addition their existance make such application more difficult and time consuming. Attempts to reduce seeding by physically modifying castor derivatives are described in U.S. Pat. No. 3,203,820.
The molecular structure of natural castor oil is a triglyeride with three pendant carbon chains. Generally, each carbon has a double bond at the 9,10 position and a hydroxyl group on the 12th carbon. Castor oil in nature has a hydroxyl value of approximately 160-165 with a fatty acid distribution of approximately 89% C.sub.18 OH and 9% C.sub.18 ; that is, not all the carbon chain lengths in natural or untreated castor oil contain an OH group; only about 90% of said chains on average do so. The various components are described in Table 1.
TABLE 1 ______________________________________ COMPONENTS OF CASTOR OIL ______________________________________ ##STR1## ______________________________________ where approximately 2% of R.sub.i = C.sub.15, 98% = C.sub.17 ; 88% of R.sub.i has OH in the 12 position and a double bond in the 9,10 position; 10% of R.sub.i has no OH, but may or may not have a double bond in the 9,10 position; and R.sub.i = R.sub.1 and/or R.sub.2 and/or R.sub.3 The hydrogens are not shown.
Castor wax can be produced from castor oil by hydrogenation, see FIG. 1, and can be described as essentially a hydrogenated molecule having no appreciable change in hydroxyl value versus the natural hydroxyl value of castor oil from which it was made. Castor oil has a natural hydroxyl value in the range of 160-168. Hydrogenation can be accomplished by many known methods and can occur as part of or distinct from other reactions involving castor oil, for example sulfonation (a reaction of castor oil with sulfuric acid) and dehydration. Hydrogenation can be partial or substantially complete as described above.